This invention is directed to the providing of a suitable hydraulic structure which is designed to be utilized as a highway edgedrain. The United States of America's total investment in its highway system exceeds $200 billion dollars, with the greatest enemy to these highways being water. The presence of undesirable levels of water in the road sub-base aggravates the deterioration of the highway. The types of pavement distresses caused by water are quite numerous and vary depending on the type of pavement system. For flexible pavement systems, such as asphalt, some of the distresses related to water either alone or in combination with temperature include: potholes, loss of aggregates, raveling, weathering, alligator cracking, reflective cracking, shrinkage cracking, and heaves (from frost or swelling soils). For rigid pavement systems, such as concrete, some of the distresses include faulting, joint failure, corner cracking, diagonal cracking, transfer cracking, longitudinal cracking, shrinkage cracking, blow-up or buckling, curling, D-cracking, surface spalling, steel corrosion, and heaving (from frost or swelling soils). Since 1976, the U.S. Department of Transportation, Federal Highway Administration, has been conducting studies aimed at solving the water problem. Since 1977, the Transportation Research Board of the National Academy of Science has been involved in similar research efforts. Ongoing studies by both these organizations have attempted to address this serious problem.
Moisture in pavement systems can come from several sources. Moisture may permeate the sides, particularly where coarsegrained layers are present or where surface drainage facilities within the facility are inadequate. The water table may rise; this can be expected in the winter and spring season. Surface water may enter joints and cracks in the pavement, penetrate at the edges of the surface, or percolate through the surfacing and shoulders. Water may move vertically in capillaries or interconnected water films. Moisture may move in vapor form, depending on adequate temperature gradients and air-void space. Moreover, the problem of water pavement systems often becomes more severe in areas where frost action or freeze-thaw cycles occur, as well as in areas of swelling soils and shales.
Once the sub-base becomes appreciably saturated, the highway literally is floating on a bed of saturated base material. The water problem is further aggravated by a phenomenon known as "pumping". The surface of a highway, whether it be of an asphalt or concrete composition, has a significant amount of force exerted on it by larger vehicles, such as semi-tractor trailers. This exertion of force actually causes the pavement to deflect slightly, wherever cracks or underlying voids are present with respect to asphalt roads, and wherever joints, faults or underlying voids are present with respect to concrete roads. This deflection of the pavement, however slight, causes a pumping movement with respect to the water trapped in the sub-base. Part of this pumping of water occurs laterally through the sub-base only, resulting in the washing away of fine soil particles, which over time significantly weakens the sub-base.
More important, however, is the movement of water immediately beneath the pavement surface. This movement of water tends to erode the area under the pavement, causing voids and ultimately leading to pavement failure. Additionally, the velocity of the water flow carries away small portions of the lower pavement surface. Studies by the French government have shown that the velocity of the water flow generated by "pumping" can reach up to 200 mph. Thus, the problems caused by water cannot be underestimated. An example of how acute these problems can become, is vividly shown by the fact that in 1981, the United States Congress launched a federal investigation into the deterioration of Interstate 10 in Florida, which had been destroyed within 6 years of its date of installation by the interaction of water with the road surface.
Recognition of the problem water poses for roads is not new. However, the two traditional approaches to the problem, i.e. better methods of sealing the road surface, and improved structural design of the pavement, have proved futile in combatting roadway deterioration. Thus, it has only been in recent years that attention has been directed to the merits of edgewater drainage.
The earliest attempts at trying to combat the problem of water through proper edgewater draining of highways commenced in earnest in the early 1970's, when sections of 4 inch round plastic pipe manufactured according to the teaching of Sixt, U.S. Pat. No. 3,699,684 were laid on top of a sheet of polypropylene fabric. The pipe was then covered with gravel, with the fabric then being folded over the gravel, and covered by a cement or asphalt cap. Other examples of subterranean drain design, such as Delattre, French Pat. No. 2,384,901, Healy et al., U.S. Pat. No. 3,654,765, Healy et al., U.S. Pat. No. 3,563,038 and Glasser et al., Great Brit. Pat. No. 2,056,236 were incapable of accommodating the flow present in highway edgedrains and thus proved of no help in solving the problem. Additionally, these drain designs are rigid and not bendable, thus requiring excavation of sufficiently long trenches so that an entire length of drain can be installed. Moreover, there is the problem of matting and lack of structural integrity. Finally, the surface area of the drain capable of being in direct contact with the sub-base for purposes of support was minimal due to the presence of the cylindrical conduit. The problem relating to surface area also confronted Sixt, U.S. Pat. No. 3,830,373 and was aggravated by the fact that the surface area for intercepting sub-surface water was limited to approximately the diameter of the conduit.
In approximately 1983, the Monsanto Corporation introduced its answer to the edgedrain problem in the form of its Hydraway.RTM. edgedrain, a flexible composite product with fabric bonded to a polyethylene core. U.S. Pat. No. 4,572,700 was granted in connection with the Monsanto.RTM. product. Other companies have attempted to provide strong, efficient hydraulic structures for use as highway edgedrains. Examples of other companies and their respective products include Burcan Manufacturing, Inc. and its Stripdrain.TM. and the American Wick Drain Corporation and its product, Akwadrain.TM..
Unfortunately, all of these recent attempts at providing efficient hydraulic structures have resulted in products which are relatively fragile and have a tendency to encounter dimensional creep. Dimensional creep causes the hydraulic structure to slowly move vertically when horizontal stress is applied, thereby sacrificing structural integrity and forming voids. Dimensional creep exacerbates problems with matting, as well as accelerating roadway deterioration. Further, they often utilize fabric which, depending on the adjoining soil, may become blinded with soil particles or may allow too much material to pass through resulting in loss of sub-base support. Additionally, due to their structure, their fabric has a tendency to mat down, thereby blocking flow channels and causing a decreased flow capability. Furthermore, they are characterized by a labyrinth-like staggered flow channel, as opposed to one which is essentially free-flowing.